Automatically controlled instrument systems having carriages which move in two coordinate directions over a work surface of a table are well known. Typically, a first carriage traverses the table in one coordinate direction parallel to the work surface and a second carriage mounted on the first carriage moves relative to the first carriage in the other coordinate direction. When an instrument is mounted on the second carriage, composite movements of both carriages allow the instrument to be translated to any point over the region of the work surface traversed by the carriages. Accurate positioning of the carriages and, consequently, of the instrument, is achieved by numerical control which may operate either from an on-line data generator or from previously programmed data. Such a numerical control system is described in U.S. Pat. No. 3,887,903. Additionally, such instrument systems can be operated manually to position an instrument to predetermined locations.
Automatically as well as manually controlled systems of this type may be employed with a wide variety of instruments. These instruments may include, for example, plotting pens or styli for drawing graphical representations of information on paper. Additionally, these instruments may include cutting or drilling tools including, routers and water jet cutters for cutting a variety of sheet material, such as fabric and plastics.
In such systems, it is desirable to accurately position the carriage in both coordinate directions. Particularly, where a second carriage is mounted on a beam driven by the first carriage and moves relative to the first carriage, it is desirable that the second carriage slidably moves on the beam with minimal displacement in directions other than the coordinate direction of movement. The second carriage must engage the beam for free, slidable movement thereon over the entire length of the beam independent of dimensional variations present in the beam track. Due to variation in the components which mount the carriage to the beam or track, the instrument being carried by the second carriage may not perform consistently, as desired, over all areas of the work surface of a table. For example, where there are variations in the width of the track upon which the carriage rides, in narrow places, the instrument will be slowed as it moves over the surface of the table to thereby create an inaccurate plot or cut. Additionally, where the track is wider than specified, the instrument is not maintained in the desired perpendicular position to the work surface, also resulting in an inaccurate plot or cut. Therefore, it is desirable that the carriage for mounting an instrument to a track have the capability of compensating for any dimensional variations in the track.
Previously developed carriages have utilized complicated spring mechanisms interconnected to wheels to compensate for variations in the width of a track. Such systems have required numerous parts requiring frequent replacement due to damage and wear. Furthermore, such carriages have not sufficiently compensated for variations in the width of a track resulting in inaccurate operation of the instrument.
A need has thus arisen for a carriage for carrying an instrument which maintains the instrument in a predetermined position relative to the carriage regardless of variations in the track upon which the carriage rides.